Even the smallest window AC units I have seen usually recommend being on at least a dedicated 15 amp circuit. Because they use about 10 amps of 120. Your service is only allowing about 15 amps of 240 per apartment. That is just barely enough to get by. Not allowing air conditioners could just have them using a bunch of large fans and they draw a decent amount too. I find sometimes it's easier to maintain a temp in a building than at a certain part of the day try to get it cooled down.

Thanks for that.

As I understand it the consumption of a window a/c unit can be calculated by dividing the BTU's by the EER, so an 11,000 BTU unit with a 9.7 EER would draw more than 10 amps. But the 5,200 BTU EnergyStar units which I recommend for the 110 sq. ft. bedrooms would consume only 485 watts (and draw 4.4 amps @ 110V).

In the past I have asked tenants to turn off their a/c units during the day when they are at work and when the highest time-of-use energy rates apply, notwithstanding that it occurs to me that this could result in a significant peak demand at suppertime when tenants return from work. However, a bit of work with the spreadsheet suggests that this needn’t be a concern insofar as an analysis of last summer’s consumption data shows that peak usage normally occurs in the evening, and most often between 9:00 pm and 10:00 pm. (During the summer of 2011 usage only exceeded 6 KWH on six occasions, and in half of these cases the peak hourly usage occurred between 9:00 pm and 10:00 pm). Given the cost difference between peak and off-peak rates I am guessing that it is still better to have the tenants turn the units off in the afternoons when they are not home.

That was my original plan, but this would require that the building be in compliance with all aspects of the current Code, which would be fraught with difficulty.

Firstly, Code would require that each apartment be on a separate “time-of-use” revenue meter and be billed separately. This is intended to encourage tenants to practice conservation, however under our tenant-protection legislation I cannot require existing tenants to pay for their electricity. Accordingly I would be paying for 13 accounts and would incur almost $3,000 annually in additional account service charges. I could required new tenants to pay for the own electricity, however most tenants prefer to rent with the utilities included. (In any case, my apartments don't often turn over).

At present the electrical panels share the utility room with the boiler. Code would require a separate room for the panels and meters, so I could be forced to repurpose the laundry room as an electrical vault. I expect that the laundry room is more important to most of the tenants than air conditioning is, and to the extent that having the panels in a separate room might improve building safety somewhat I expect that the risk imposed upon tenants… most of whom do not own cars and would need to walk the five blocks to the laundromat… makes it an unsatisfactory trade-off. (And I would lose more than $200 per month in laundry revenue).

Finally, there is some doubt as to whether the transformer(s) on our street are up to the task, and the utility cannot advise me on this without doing some testing (at my expense). But it is my understanding that any needed upgrades to the utility’s infrastructure would be at my expense (and I presume that transformers are expensive). And notwithstanding that tenants might be agreeable to paying higher rents for a more robust electrical system the tenant-protection legislation limits any agreed-upon increase to 3%.

As for your exact situation, I cannot comment because I am not familiar with service sizing in Canada. There are a few professionals from Canada on these boards who will be able to give you much more information. If I was forced to give an opinion, it would be that the service is at full load according to calculations.

Thanks for that.

The calculations which are used in order to determine load for Code purposes may differ depending upon the jurisdiction, but in any case I'm not convinced that I should rely on prescriptive calculations where I am attempting to determine actual loading rather than theoretical loading. For example, allocating 3 watts per square foot of floor area for general usage would result in a theoretical load of 1,200 watts for my hallways, notwithstanding that they are well-illuminated with ten LED fixtures which consume 80 watts in total. In the laundry room, where the lights are on motion sensors and consume perhaps 0.01 KWH per day I would need to allocate 50 times that much for general usage (in addition to the specific appliance loads).

Obviously if I wanted to build an addition or make other fixed changes I would need to use presciptive calculations in order to get a permit, but the Codes do not address tenants using consumer electronics such as window air condtioners in their apartments (and the wiring in most of the apartments is up to Code). Historically the building's usage is permissable and there is no law that says that when "X" number of tenants buy plasma TVs (some of which consume more power than air conditioners) that I am required to upgrade the service.

In the past couple of years we’ve reduced our annual electrical consumption by 40% by improving the efficiency of our lighting, replacing many of the electric stoves with gas stoves, replacing fridges and by encouraging tenants to be frugal with their energy consumption. For the most part this had everything to do with cost-savings, so I have not re-lamped lights which are likely to burn for less than three hours per day where the return on investment would be unattractive. But it occurs to me that I could reduce our potential peak demand by at least 2 KW by re-lamping every remaining fixture with LEDs.

I could also replace a couple of the stoves with gas stoves, however this is likely to have more impact on the prescriptive calculations than on the actual peak demand, which as I mention in another post peaks between 9:00 and 10:00 pm when it is unlikely that tenants will be using their stoves.

How many tenants do you think you would lose if you did not allow them to install air conditioners?

Since you had electric stoves and can replace them with gas, you can gain more "headroom" regarding overall power consumption. Still, the average consumption over all 12 apartments allowed is 33 amps (at 120 volts) per apartment assuming a perfect balance between the two hot legs of the service. You figure out the rest given that the maximum ampere air conditioner unit you will allow will be 10 amps per apartment (9 amps?, 8 amps?)

The current minimum service size for apartments in the U.S. is 60 to 100 amps at 240 volts depending on the apartment size and the city. Your load calculation numbers will take into account electric versus gas stoves. Note that it is possible you need to upgrade the gas service when adding several gas stoves that were not there originally.

Since the electricity is included in the rent, you need to think about the added power consumption with air conditioners in use. To avoid having to come homeand then wait for the apartment to cool down in the late afternoon with a smaller (8 amp?) AC unit, some tenants may leave it on all day. To get around this problem you may well decide not to allow any more air conditioners and the rest of the argument in this thread then becomes academic.

__________________The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.

If you get me a list of what you've got in the apartments and what they draw then i can probably figure it all out for you. A 5200 btu window a/c unit typically draws around 5 amps. I can do out a load calc for an apartment to find out how far under powered you are as well. Typically the apartments will have a 60A panel with the stove taking up most of it and only 2 15a circuits for the rest of the place and a dedicated line for the fridge. I lived in an older building for quite some time and this was how it was as well. Something you could do is to throw an ampmeter on the incoming line to see what the draw is at peak times. Realistically speaking and all legalities aside other than the stoves most of your apartments will draw an average of around 10A each at any given time with airconditioners in each one.

__________________
Sarcasm is my friend
I'm here to learn too, i do mostly commercial/industrial/new construction and this place is a great way to pick up tips on residential from some good electrical minds. Excuse the spelling, my phone has a mind of it's own.

So for 12 units the peak additional draw would be 102 - 112 Amps @ 120V. Overall, you should have adequate capacity. Without knowing the wiring of each apartment, I can't comment on adequacy of the wiring. Ideally, a room air conditioner should be on a its own circuit.

In the US it is very common to include a provision in the lease concerning room A/C.

All units must be ENERGY STAR rated (alt: have an EER 9.7 or greater), and less than 5 years old. The ENERGY STAR and EnerGuide labels must remain attached to the unit or a copy provided to management.

A/C units must be removed from the windows and windows properly sealed between 1 Oct and 30 Apr.

The lesee is responsible for safe and secure installation, including sealing to prevent infestation by pest or vermin.

Lesee is responsible for any damage to window, apartment or complex caused by installing or operating a room air conditioner.

Yes, I'd assumed that in order to air condition the entire apartment the tenant would need a 5,200 BTU unit in the bedroom (110 to 125 sq ft) and a 6,000 BTU unit in the living area. (Most have open-concept living/dining/kitchen areas of about 250 sq. ft.). So I'd need about 10 amps of EnergyStar air conditioning for an entire apartment.

To date no one has asked to install more than one unit, and four of the five presently installed are in the bedrooms. I ought to have mentioned that I charge an energy surcharge of about $85 per machine, per season, so this is a bit of a disincentive.

My leases simply prohibit air condtioners without my approval, and I inform tenants that I will only approve EnergyStar units.

How many tenants do you think you would lose if you did not allow them to install air conditioners?

A valid question, and one which takes us to the crux of the matter.

I market myself as a "green" landlord, which allows me to attract tenants who are likely to be stingy with their consumption. When CF bulbs came into common usage 15 years ago I used them in some common areas but felt that the light they emitted was too unattractive for living spaces, and was surprised to discover that a few tenants had re-lamped their apartments with CF bulbs at their own expense. And when I drove past the building during "Earth Hour" last year it was in almost total darkness.

In this context, when I have an availability I invariably have multiple applications and most applicants are well-qualified, so if a prospective tenant indicates that air conditioning is important to them I would move their application to the bottom of the pile anyway.

So no, I do not feel that I need to jump through hoops (upgrade to 400 amps) in order to meet the needs of my tenants, when I can much more affordably attract tenants with modest needs.

To avoid having to wait for the apartment to cool down in the late afternoon with a smaller (8 amp?) AC unit, some tenants may leave it on all day.

As I mention above, I charge an energy surcharge... more specifically it is a monthly charge which applies from June to September. I inform tenants that so long as consumption is reasonable I will waive the September portion of the surcharge. So aside from the fact that most of my tenants are likely to be responsible because they want to reduce our carbon footprint, those not motivated by such considerations will find it in their financial self-interest not to leave their machines running all day. (And I have, in fact, always waived the September surcharge).

If you get me a list of what you've got in the apartments and what they draw then i can probably figure it all out for you. A 5200 btu window a/c unit typically draws around 5 amps. I can do out a load calc for an apartment to find out how far under powered you are as well. Typically the apartments will have a 60A panel with the stove taking up most of it and only 2 15a circuits for the rest of the place and a dedicated line for the fridge. I lived in an older building for quite some time and this was how it was as well. Something you could do is to throw an ampmeter on the incoming line to see what the draw is at peak times. Realistically speaking and all legalities aside other than the stoves most of your apartments will draw an average of around 10A each at any given time with airconditioners in each one.

Yesterday we had our annual fire department inspection, so I had a chance to visit each apartment. I did not have time to do a precise audit, but was able to get a feel for what my tenants use.

These are small apartments and most of the tenants are young, single, university grads with entry-level white-collar professions and big student loans to pay off. I saw surprisingly few desktop computers, but virtually everyone has a laptop. But they don't seem to be using them with external monitors (as i do). Most (but not all) have TVs, but these are likely to be LCDs 32" or smaller, most of which now draw less than 100 watts. Most have cable receivers or PVRs.

Other than the usual coffee-maker, microwave oven and toaster (and one or two toaster ovens) I did not see a lot of kitchen gadgets. Only a few had accessory lighting fixtures, and many of these had CF bulbs.

Most units have ceiling fans, and most of these have lights which typically house a single 40-watt bulb... although I have two which take 75 watt halogens and two which take 100 watt halogens.

With regard to permanent lighting fixtures, I've re-lamped most units with CF or LED bulbs. A typical (re-lamped) one-bedroom unit might use 150 watts for illumination assuming that every light in the apartment turned on.

So even with their TVs and computers, unless they are using their kitchen appliances they would be hard-pressed to draw more than 4 amps, or about 9 amps with a single air conditioner running. It is, of course, entirely possible that they could turn on their toasters, microwaves and coffee makers at the same time. In this context, we've rewired most of the individual apartments according to Code, so all of the countertop outlets are split duplex and all of the apartment services are 60 amp. BTW, the electric stoves do not run off these pony panels. When I bought the building the apartments did not have their own panels and the stoves were wired directly into a separate panel in the utility room, so we left the stove circuits intact.

So notwithstanding the use of toasters and other high-wattage kitchen appliances the electrics within the units can handle the task, so it is a matter of whether every tenant wants to make toast at the same time.

As an aside, we also provided a separate 15 amp dedicated outlet underneath at least one window in every living room and bedroom in anticipation of air conditioners.

As I've mentioned, I've been analysing 2 1/2 years of hourly consumption data. While I recognize that there is an important difference between peak hourly usage and peak loading, I'll assume (perhaps incorrectly, of course) that peak demand would not be more than 150% of peak hourly usage.

At breakfast time hourly consumption averages about 2.75 KWH and never exceeds 4.1 KWH. This is when I would expect the short-term spikes as tenants use their hair dryers, perhaps iron their frocks, and make their coffee and breakfast (although I expect that for many of these tenants breakfast is more likely to be granola with yogurt rather than bacon and eggs). If I allow for double the maximum hourly usage we're still only at about 72 amps @ 115V..

Between 6:00 pm and 7:00 pm consumption averages 3.3 KWH and never exceeds 6.0 KWH. If we allow an extra 50% for short-term loading we're at 78 amps.

It is between 9:00 pm and 10:00 pm in the summer that we see our greatest consumption. Since four of the five air conditioners are in bedrooms we can assume that tenants turn them on a few hours before bed. In the summers of 2010 and 2011 we saw consumption max out at 6.75 KWH both years, and while it is unlikely that tenants are going to be using cooking appliances at this time of evening during the warmest evenings of the year, we can still allow an extra 50% and we're still under 90 amps.

Perhaps I've not properly accounted for the five 240V stoves. I think that the prescribed calculations would require that I allow 9 KW for each, and use 40% of the total. This gives the stoves 75 amps @ 240V. This leaves us with (assuming perfect balance) 125 amps (250 amps @ 240V) for general usage. If my calculation (guesstimate) that our peak load never exceeds 90 amps is correct, then the theoretical 160 amp remaining capacity should give me comfort.

At the beginning of this conversation I was wondering if I could add one or two additional air conditioning units of 6,000 BTU or less. Unless I have misunderstood, based upon what I have gleaned from this thread and from my data analysis it seems to me that I could add several more units without concern.

(BTW, yesterday I re-lamped another apartment, swapping out 560 watts of halogen lighting for 50 watts of LED lighting. It occurs to me that the 510 watts saved is more than would be consumed by one of the 5,200 BTU units).

the stoves would draw around 187A IF the ovens and all burners were on on each of them all at once, that's assuming your 9kw draw per stove. I did some quick math and at the 6.75kwh peak for the one hour at night during the summer your only using around 56A for that hour. Honestly i think your fine adding another AC or two, use common sense. While it may not be totally legal load calc. wise and i'm sure people will jump all over this one i highly doubt it's going to cause any overloading.

__________________
Sarcasm is my friend
I'm here to learn too, i do mostly commercial/industrial/new construction and this place is a great way to pick up tips on residential from some good electrical minds. Excuse the spelling, my phone has a mind of it's own.

Use a portable clamp-on ammeter so you only need one. The readings will be good enough for this purpose even though less accurate than a wired-in ammeter.

It has jaws like an alligator clip that go over a wire, over insulation and all.

__________________The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.

a decent clamp on will cost you a few bucks, around $100 or so, but it will also function as a multimeter and being as you have your own building it's not an unwise investment. You'll get years of use out of it. Fluke makes a decent "fork" style one but it's a little pricey.
here's one at home depot that would work for you, i prefer cat IV but this will work just fine for your application.http://www.homedepot.ca/product/clam...cat-iii/930198

if your really nervous about it i can send you my email, i'm in toronto as well and can give you some better instructions.

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__________________
Sarcasm is my friend
I'm here to learn too, i do mostly commercial/industrial/new construction and this place is a great way to pick up tips on residential from some good electrical minds. Excuse the spelling, my phone has a mind of it's own.